Re: [PATCH] drop_caches: Allow re-enabling message after disabling

Joel Granados
2025-03-13T15:54:07Z

On Thu, Mar 13, 2025 at 04:46:36PM +0100, Joel Granados wrote:
> After writing "4" to /proc/sys/vm/drop_caches there was no way to
> re-enable the drop_caches kernel message. By removing the "or" logic for
> the stfu variable in drop_cache_sysctl_handler, it is now possible to
> toggle the message on and off by setting the 4th bit in
> /proc/sys/vm/drop_caches.
>
> Signed-off-by: Joel Granados <joel.granados@kernel.org>
> ---
> Documentation/admin-guide/sysctl/vm.rst | 2 +-
> fs/drop_caches.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> index f48eaa98d22d2b575f6e913f437b0d548daac3e6..75a032f8cbfb4e05f04610cca219d154bd852789 100644
> --- a/Documentation/admin-guide/sysctl/vm.rst
> +++ b/Documentation/admin-guide/sysctl/vm.rst
> @@ -266,7 +266,7 @@ used::
> cat (1234): drop_caches: 3
>
> These are informational only. They do not mean that anything is wrong
> -with your system. To disable them, echo 4 (bit 2) into drop_caches.
> +with your system. To toggle them, echo 4 (bit 2) into drop_caches.
>
> enable_soft_offline
> ===================
> diff --git a/fs/drop_caches.c b/fs/drop_caches.c
> index d45ef541d848a73cbd19205e0111c2cab3b73617..501b9f690445e245f88cbb31a5123b2752e2e7ce 100644
> --- a/fs/drop_caches.c
> +++ b/fs/drop_caches.c
> @@ -73,7 +73,7 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
> current->comm, task_pid_nr(current),
> sysctl_drop_caches);
> }
> - stfu |= sysctl_drop_caches & 4;
> + stfu = sysctl_drop_caches & 4;
> }
> return 0;
> }
>
> ---
> base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6
> change-id: 20250313-jag-drop_caches_msg-c4fbfedb51f3
>
> Best regards,
> --
> Joel Granados <joel.granados@kernel.org>
>
>
In case you are curious:
This is a V3 of what was discussed in https://lore.kernel.org/20250216100514.3948-1-rwchen404@gmail.com
My bad for forgetting to tag it V3 :(.
Best

--

Joel Granados